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Milky Way - Wikipedia

Milky Way

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The Milky Way or Milky Way Galaxy1, or simply the Galaxy,2 is the galaxy that includes the Solar System, with the name describing the galaxy’s appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galaxy, which are so far away that they cannot be individually distinguished by the naked eye.

The Milky Way is a barred spiral galaxy with a D isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years),[^13] but only about 1,000 light-years thick at the spiral arms (more at the bar). Recent simulations suggest that a dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years (613 kpc).34 The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, forming part of the Virgo Supercluster which is itself a component of the Laniakea Supercluster.56

It is estimated to contain 100–400 billion stars78 and at least that number of planets.910 The Solar System is located at a radius of about 27,000 light-years (8.3 kpc) from the Galactic Center,11 on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The Galactic Center is an intense radio source known as Sagittarius A﹡, a supermassive black hole with a mass of 4.100 (± 0.034) million solar masses.1213 The oldest stars in the Milky Way are nearly as old as the universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.14

Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the universe.15 Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis,16 observations by Edwin Hubble in 1923 showed that the Milky Way was just one of many galaxies.

Printed 2026-06-28.

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Footnotes

  1. Some authors use the term Milky Way to refer exclusively to the band of light that the galaxy forms in the night sky, while the galaxy receives the full name Milky Way Galaxy. See for example Laustsen et al., Pasachoff, Jones, van der Kruit, and Hodge et al. ↩

  2. Poggio, E.; Drimmel, R.; Andrae, R.; Bailer-Jones, C. A. L.; Fouesneau, M.; Lattanzi, M. G.; Smart, R. L.; Spagna, A. (2020). “Evidence of a dynamically evolving Galactic warp”. Nature Astronomy. 4 (6): 590–596. arXiv:1912.10471. Bibcode:2020NatAs…4..590P. doi:10.1038/s41550-020-1017-3. S2CID 209444772. ↩

  3. Croswell, Ken (March 23, 2020). “Astronomers have found the edge of the Milky Way at last”. ScienceNews. Archived from the original on March 24, 2020. Retrieved March 27, 2020. ↩

  4. Dearson, Alis J. (2020). “The Edge of the Galaxy”. Monthly Notices of the Royal Astronomical Society. 496 (3): 3929–3942. arXiv:2002.09497. Bibcode:2020MNRAS.496.3929D. doi:10.1093/mnras/staa1711. S2CID 211259409. ↩

  5. “Laniakea: Our home supercluster”. YouTube. September 3, 2014. Archived from the original on September 4, 2014. ↩

  6. Tully, R. Brent; et al. (September 4, 2014). “The Laniakea supercluster of galaxies”. Nature. 513 (7516): 71–73. arXiv:1409.0880. Bibcode:2014Natur.513…71T. doi:10.1038/nature13674. PMID 25186900. S2CID 205240232. ↩

  7. “Milky Way”. BBC. Archived from the original on March 2, 2012. ↩

  8. “How Many Stars in the Milky Way?”. NASA Blueshift. Archived from the original on January 25, 2016. ↩

  9. Cassan, A.; et al. (January 11, 2012). “One or more bound planets per Milky Way star from microlensing observations”. Nature. 481 (7380): 167–169. arXiv:1202.0903. Bibcode:2012Natur.481..167C. doi:10.1038/nature10684. PMID 22237108. S2CID 2614136. ↩

  10. “100 Billion Alien Planets Fill Our Milky Way Galaxy: Study”. Space.com. January 2, 2013. Archived from the original on January 3, 2013. Retrieved January 3, 2013. ↩

  11. Gillessen, Stefan; Plewa, Philipp; Eisenhauer, Frank; Sari, Re’em; Waisberg, Idel; Habibi, Maryam; Pfuhl, Oliver; George, Elizabeth; Dexter, Jason; von Fellenberg, Sebastiano; Ott, Thomas; Genzel, Reinhard (November 28, 2016). “An Update on Monitoring Stellar Orbits in the Galactic Center”. The Astrophysical Journal. 837 (1): 30. arXiv:1611.09144. Bibcode:2017ApJ…837…30G. doi:10.3847/1538-4357/aa5c41. S2CID 119087402. ↩

  12. Overbye, Dennis (January 31, 2022). “An Electrifying View of the Heart of the Milky Way – A new radio-wave image of the center of our galaxy reveals all the forms of frenzy that a hundred million or so stars can get up to”. The New York Times. Archived from the original on January 31, 2022. Retrieved February 1, 2022. ↩

  13. Heyood, I.; et al. (January 28, 2022). “The 1.28 GHz MeerKAT Galactic Center Mosaic”. The Astrophysical Journal. 925 (2): 165. arXiv:2201.10541. Bibcode:2022ApJ…925..165H. doi:10.3847/1538-4357/ac449a. S2CID 246275657. ↩

  14. Bond, H.E.; Nelan, E. P.; VandenBerg, D. A.; Schaefer, G. H.; Harmer, D. (February 13, 2013). “HD 140283: A Star in the Solar Neighborhood that Formed Shortly After the Big Bang”. The Astrophysical Journal. 765 (1): L12. arXiv:1302.3180. Bibcode:2013ApJ…765L..12B. doi:10.1088/2041-8205/765/1/L12. S2CID 119247629. ↩

  15. “Milky Way Galaxy: Facts About Our Galactic Home”. Space.com. Archived from the original on March 21, 2017. Retrieved April 8, 2017. ↩

  16. Shapley, H.; Curtis, H. D. (1921). “The Scale of the Universe”. Bulletin of the National Research Council. 2 (11): 171–217. Bibcode:1921BuNRC…2..171S. ↩

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